A greenhouse lets you start seedlings earlier in the season so they’re well developed when the weather outside becomes warm enough to set them out. Greenhouses also enable gardeners to grow crops later in the season and further extend the harvest.

In warmer climate zones, or with insulated or heated models for colder regions, a greenhouse enables you to grow cool and warm weather crops all year.

Greenhouses protect fragile new sprouts and young seedlings from weather events like late frosts, cool spring weather, heavy rains, wind and hail.

Hidden pests in the subsoil such as wireworm, slugs and pill bugs may emerge at night and damage fragile new sprouts and young seedlings. Airborne pests such as cabbage moths can destroy sprouts of Brassicas such as broccoli, cauliflower, cabbage, kale, and brussel sprouts.

Bird activity increases during spring, and many bird species will dig and scratch into the upper layer of soil in search of bugs and worms. This disturbs germinating seeds. Emerging sprouts are also susceptible to bird predation.

Greenhouses are commonly used for growing starters in pots for transplanting outdoors, or for growing plants to maturity in containers or deep shelves. Plants can also be grown directly in the ground in greenhouses, which enables crops susceptible to airborne diseases, like tomatoes, to grow larger.

The controlled environment of a greenhouse results in a high rate of success with seed germination. This lets you grow as many plants as you like, without having to pay for ‘starters’ at your nursery center.

There are some drawbacks to gardening in greenhouses which can be mitigated by choosing the right greenhouse and greenhouse accessories for your growing region.

Since seasonal rains will not reach your greenhouse plants, you need to pay attention to soil moisture levels. Plants grown in containers have the benefit of being well-drained, but have the liability of drying out faster than plants grown outdoors in the ground. There are automatic watering systems available as greenhouse accessories which can address watering needs.

An unvented greenhouse can get too hot in summer and cause plants to wilt or die. Most greenhouses provide ventilation, but manual vents may be left closed at times. Automatic vents are a great solution, and available as accessories with most greenhouse designs.

These small and mid-size greenhouses are very popular for propagating seeds and starter plants which will be transplanted outdoors to garden beds. The starter, or hobby, greenhouse also doubles as a potting shed, where garden supplies can be kept under cover, transplants can be repotted, and harvested crops can be brought in to cure and be processed for winter storage. These greenhouses often have clear or semi-diffused coverings, since the direct light favors seed propagation. Click here to see our selection of starter greenhouses.

These are larger greenhouses, often with adjustable shelving, for growing crops full-term indoors under shelter. Diffused or semi-diffused coverings are common for these larger greenhouses. These are all-purpose greenhouses, good for propagating seeds, great for indoor growing of crops, and spacious enough for curing harvested crops and preparing them for storage. Click here to see our grower greenhouses.

Another way of differentiating the types of greenhouse is by temperature level. Whichever type of greenhouse you purchase, you have the choice of three basic ways of approaching greenhouse gardening: hot, warm and cool.

Or ‘hot house’, these greenhouses have a stable temperature in the range of 65 – 70 degrees or higher. This temperature range is used to grow exotic and tropical plants. Heaters and grow lights are usually needed to maintain this level of heat.

Warm greenhouses have a stable temperature in the range of 50 – 55 degrees. In this temperature range, you can grow plants which you would grow in your outdoor flower or vegetable garden. You may need to use grow lights or heat lights to meet the heating needs during the winter night months.

Or ‘frost-free’ greenhouse, these greenhouses have a stable temperature in the range of 40 – 45 degrees. This is an ideal temperature range for a ‘nursery’ greenhouse, where you will be germinating seeds and raising your own starter plants and vegetables for the summer months. You generally don’t use grow lights or heat lights in this environment.

Tempered glass panes are very strong and impact-resistant, and will withstand expansion and contraction during seasonal temperature changes. Single-pane thickness of 3mm is adequate for greenhouses, but 4mm thickness is stronger and provides additional insulation value. The edges must be protected during installation, as they will shatter the pane if hit with a hard object. Tempered glass is more expensive than polycarbonate panels, but it is more durable and scratch-resistant. Tempered glass is clear, and provides no diffusion.

Fiberglass is translucent and provides well-diffused light. Fiberglass retains heat more efficiently than glass. Fiberglass greenhouses are usually corrugated to provide rigidity. The outer gel coat will become sun-baked, often within 6 – 10 years depending on exposure. The surface eventually becomes etched and yellowed, and dirt and debris can collect in the valleys.

UV-treated polyethylene film is commonly used to cover large commercial greenhouses because it is relatively inexpensive and easy to maintain. It is translucent, which provides a semi-diffused light, and retains heat well, especially when double-walled. Polyethylene films only last 3 – 5 years in outdoor conditions, and are subject to stretching and sagging in windy locations or after being loaded with snow. This material can be poked through by falling branches, or torn during winds if not well secured.

Twin-wall, high-density polyethylene sheets are more flexible than polycarbonate panels, more rigid than polyethylene film, and come in rolls or sheets as covers for greenhouses. The material is 2-ply, with inner walls which separate the sheets and create an internal air space. This provides excellent insulation value. Twin-wall polyethylene is infused with UV inhibitors and provides soft, diffused light while letting about 75% of natural light to pass through. Twin-wall polyethylene is milky white, or opaque, in appearance. An example of twin-walled polyethylene is the Solexx line of greenhouses.

Durable and lightweight, UV-treated polycarbonate is a modern, high-quality covering material for greenhouses. Available in different thicknesses, polycarbonate panels provide the clarity of glass but are not as strong or scratch resistant as tempered glass panels. Single-walled polycarbonate lacks the heat retention and strength of multiwalled polycarbonates, and single-wall polycarbonate provides no light diffusion. Polycarbonate coverings have a relatively long lifespan of 15 years or longer in most regions.

Multiple-walled polycarbonate greenhouse coverings are very popular because they have internal air spaces which provide added strength and excellent insulating values. Of particular importance, multiwalled polycarbonates provide diffused light.

This covering has all the benefits of twin-walled polycarbonate, but superior strength and heat retention qualities. It is especially useful in cold climates for year-round indoor gardening. Triple-wall polycarbonate will withstand heavy snow loads and freezing without cracking or becoming distorted.

Insulation values of polycarbonate greenhouse glazing – The image to the right above shows the construction and relative thickness of available multi-panel polycarbonate glazing used for greenhouse cover panels.

Note: The vertical separators have three functions: they add structural strength to the panel, increase insulation value by providing an air space, and serve to break up, or diffuse, the light passing through the panels.

Aluminum provides a strong, lightweight frame that will not rust. It is the most widely used material for greenhouse frames, and it has a very long life span. Aluminum frames commonly have extruded channels which provide a perfect fit for inserted covering panels. Aluminum is not an insulative material, so there will be some heat loss through the framing. Powder-coated aluminum retains a smooth outer finish as well as providing different colors.

Galvanized steel frames, usually tubular, are extremely strong, long lasting, and low cost. Because of steel’s inherent strength, minimal structure is required for framing, which results in additional light getting through to the plants. Polyethylene film is often used for covering steel framing because other covering materials require fastening systems which do not lend themselves to steel frameworks. Steel frames are heavy, which helps the greenhouse remain stable in windy conditions, but the weight makes transporting and assembling the greenhouse more difficult. Steel is usually used for large commercial greenhouses.

Plastic frames have become popular because they are attractive, less expensive than aluminum and do not conduct heat out of the greenhouse as much as steel or aluminum. Plastic frames lack the strength of metal frames, so they are used primarily for smaller greenhouses which have shorter dimensions. Plastic frames are often designed to be used with polycarbonate panels.

Wood greenhouse frames are often used in do-it-yourself greenhouse building projects. Wood can provide an aesthetically pleasing appearance and sufficient strength and durability. However, wood is susceptible to rot, so the construction should ensure that the wood does not contact the ground or any moisture holding surfaces.

Greenhouses usually come with opening vents which are essential to controlling interior heat. Solar-powered automatic louvers are available which enable the gardener to have a life outside the garden. These louvers will open and shut according to preset heating levels, and are a gardener’s best assurance that plants won’t be lost to overheating.

We have lost entire sets of seedlings because we forgot to water them in time. Drip-irrigation systems, drip tape (flat hose with tiny holes), and soaker hoses can be set on inexpensive battery-operated timers which you can set onto your faucet bib. For more information, read The Absentee Gardener: How to Water Your Vegetable Garden Without Being Home

Especially useful for clear or semi-diffused greenhouses, shade cloth can be draped over the greenhouse roof to lower the inside temperature. Look for UV-stabilized knitted shade cloths with brass grommets, available in various densities. A simpler, very inexpensive method is to use split-bamboo blinds, which you can often find in shops. Shade cloths should be secured at the top of the structure and installed so that it is easy to draw them back during morning and evening hours as needed.

It’s easy to flatten young sprouts with too strong a water spray. Watering wands with adjustable nozzles are designed to let you reach to the back of seedling trays and different shelf heights without having to bend over. Fine ‘misting’ settings deliver water to germinating trays and seedlings without disturbing the soil or the tender sprouts. For more information or to purchase.

When growing your own starts from seed, you’ll need a firm surface to work on, a container to hold the potting soil and an easy way to sweep the soil spilled during potting back into the potting soil bag. Potting benches are designed with all this in mind, helping you keep the potting accessories in one place and the overall appearance of the greenhouse more organized.

Are available that will allow you reinforce the base of your greenhouse. This is useful in areas where strong winds may impact your greenhouse and potentially shift it from its foundation.

Different styles of greenhouse shelving are available which enable you to customise the interior layout of your greenhouse. Aluminum shelves with interchange heights are popular. Others can be rearranged into different geometrical shapes for attractive displays and maximizing space usage. They come in a variety of colors, with plastic liners, wheels and all sorts of different options.

Many different types of greenhouse heaters are available. Grow lights generate considerable heat for the plant, although they do not warm the soil. Some lamps or ‘toaster-coil’ types will spot heat a corner. Others, such as track systems, can be attached to the roof and heat the entire greenhouse in the winter.

Are vertical surfaces smooth? Exterior wall coverings on some designs are full (single) panels which provide continuous sheeting from top to bottom. Other designs have smaller panels set into frames which run horizontally. Any protruding horizontal lip or edge will collect dirt or grow moss over time.

It’s a common refrain among greenhouse suppliers: “Buy one size bigger than you planned.” We agree. With greenhouses, garden sheds and wood sheds, you invariably find ways to fill the space more than you expected. This is one reason so many greenhouse extension kits are on the market. If you want to stay with the original size planned, you may consider leaving room for an extension when you lay out the greenhouse ‘footprint’ in your yard.